1. Field:
This invention relates to load carrying apparatus. More particularly, this invention is directed to load lifting trucks.
2. State of the Art:
Modern day storage facilities place a premium value on the use of physical space within such facilities. In order to optimize the use of space, such facilities are conventionally organized to include a plurality of rows of pallet racking on which articles are stored. Each pair of rows is separated by an aisleway dimensioned to permit a warehouseman to pass therethrough in order to access articles located in one or the other of the opposing rows of pallet racking. It follows that economy dictates that space within a warehouse should be allocated firstly to actual storage, with space allocated to aisleways being minimized to only that required for actual passage of a lift truck.
Lift trucks of various configurations are known in the art. Conventionally, trucks include an extendible mast having a pair of outwardly extending forks mounted thereon adapted to engage, lift and otherwise convey an article to be transported. Recently, efforts have been made to modify the function of the mast to achieve enhanced operational capabilities. For example, in one type of lift truck, known as a rolling mast reach truck, the mast has been made longitudinally displaceable along the length of the truck. In other configurations, the forks have been displaceably mounted for movement laterally across the face of the mast. Each of these various mast constructions include advantages as well as disadvantages, owing to their particular operation and structure.
A conventional rolling mast-type reach truck is shown in FIGS. 1-6, positioned within a aisleway of a storage facility. Observably, the figures are not drawn to scale. The aisleway is dimensioned to have a width considerably in excess of the width of the truck, due to the necessity of providing space for the truck to maneuver into a position where it can engage, load and retract an article to be transported. In order to properly load an article onto the truck, the truck must be aligned squarely with the article. The path of a truck preparing to load an article is shown by a dotted line in FIG. 1. As shown, the truck travels longitudinally down the aisleway. It begins to turn to the left until it aligns itself squarely with the article to be loaded. Observably, this maneuver requires the aisleway to have a width (A) which is not only broader than the width (B) of the truck, but furthermore, the width (A) must be dimensionally longer than the length (C) of the truck. The width (A) must be sufficiently large to permit the truck to back up from its abutment or loading and maneuver into a position whereby the operator can drive the truck longitudinally down the aisleway.
Upon the truck reaching the condition shown in FIG. 3, the mast (D) of the truck is extended longitudinally from the truck (as shown by the arrows), thereby urging the forks under the article to be loaded.
Thereafter, the mast (D) of the truck is raised sufficiently to elevate the forks and thereby raise the article and effectively load it on the forks (FIG. 4). Thereafter, the mast is retracted toward the truck chassis (E), as shown by the arrows, bringing the loaded article with it. As shown in FIG. 4, the article and mast are retracted to a position proximate the truck chassis. Subsequently, the truck must re-execute the aforedescribed maneuver in reverse in order to bring the truck into an orientation which permits its travel down the aisleway.
As shown in FIG. 5, oftentimes the dimensions of the articles to be transported measurably increase the effective length of the lift truck after the article is loaded on the truck's forks. See length indicated generally as (F). Naturally, this increase in length due to the contribution of the article must be accounted for in determining the required width (A) of the aisleway. Oftentimes, the combined length of the truck in association with its loaded article dictate the dimensioning of an aisleway which is exceedingly wide.
One of the most critical aspects of a lift truck is its load carrying capacity. This capacity is in large part predicated on the particular geometry and function of the truck itself. For example, the truck shown in FIGS. 1-6 includes a pair of outriggers (H) which extend outwardly parallel one another longitudinally from the truck. Each outrigger engages the ground by means of a wheel mounted proximate the free end of the outrigger. When unloaded, the truck's center of gravity, identified generally by the notation (CG) is located proximate the main truck chassis as shown in FIGS. 1-6. As the forks are extended, that center of gravity is displaced longitudinally along the truck's length. When the truck actually lifts the article to be transported, the truck's center of gravity shifts dramatically toward the front of the truck as shown by the notation (CGT) in FIG. 4. If the center of gravity (CGT) shifts longitudinally beyond the point of the engagement of the outrigger wheels with the ground, indicated by plane identified by the dotted line (I), the truck is longitudinally unstable and will tip toward the loaded article and may eventually turn over. As a result, for a chassis having a given weight, the load carrying capacity of the truck is dependent on maintaining the (CGT) on the vehicle's side of the plane indicated by the dotted line (I) in FIG. 4.
Noticeably, the drawback of the conventional rolling mast truck is its requirement of relatively wide aisleways suited to permit the type of truck maneuvering necessary to orient the truck for loading and unloading an article to be transported. As previously discussed, the allocation of space for aisleways in storage facilities should preferably be minimized, since space allocated for aisleways reduces the quantity of space which may be used for storage. This follows, as a recognition that storage space, not aisleway space, is regarded as the prime and foremost priority in storage facilities.
FIGS. 8-10 illustrate the loading maneuvers of a conventional lateral turret lift truck. As shown in FIG. 8, a truck of this construction includes a pair of loading forks (J) which are oriented transverse of the longitudinal axis of the vehicle. The forks are mounted to a carriage and pivot head (K) which is constructed to be laterally displaceable along a structure (L) positioned on the front of the truck. The forks are made rotatable about the support, thereby permitting the forks to retrieve and load articles from either side of the vehicle. For example, the vehicle illustrated in FIGS. 8-10 is shown loading from the left side of the aisle, the truck could equally well load from the right side.
As shown in FIG. 8-10, the truck is driven to a location proximate the article to be loaded and the forks (J) are aligned in register with the article. A lateral translation of the forks across the face of the truck urges the forks beneath the article (FIG. 9). A lateral reversal of the forks and its supporting carriage causes the article to be retracted outwardly from its storage location in a direction generally perpendicular to the longitudinal axis (M) of the aisleway. Noticeably, the width (A) of the aisleway is determined by the length (N) of the article in combination with the depth of the fork carriage and the associated pivot head (P).
As shown in FIG. 12, the turret truck may pivot the fork carriage so as to orient the article transported collinearly with the longitudinal axis of the truck. In doing so, the operator must typically retract the article completely out of the shelf location before initiating any pivoting motion. When the article is carried in this forward facing orientation, the moment created by the article transported on the truck is maximized due to the length of the effective moment arm (R.sub.2).
There continues to be a need for a truck which requires a minimal quantity of aisle space for maneuvering during its loading and unloading operations. Further, there continues to be a need for a truck whose operation maximizes its load carrying capability.